Possible role for gp160 in constitutive but not insulin-stimulated GLUT4 trafficking: dissociation of gp160 and GLUT4 localization.
GLUT4-containing vesicles are constantly cycling in both basal and insulin-stimulated states. Our previous studies have shown that basal cycling of GLUT4 is impaired under conditions of high glucose or glucosamine and, as a consequence, GLUT4 is retained intracellularly in low-density microsomes [Filippis A., Clark, S., and Proietto, J. (1997) Biochem. J. 324, 981-985]. In addition to GLUT4 itself, a major protein component of GLUT4-containing vesicles is a glycoprotein of Mr 160000 (gp160). In all studies so far published gp160 has been co-localized with GLUT4 under all conditions. In this study, we show that retention of GLUT4 in low-density microsomes (enriched in Golgi apparatus) is associated with a decrease in gp160 levels in this compartment. A concomitant increase of gp160 in high-density microsomes (enriched in endoplasmic reticulum), demonstrates for the first time a dissociation in the localization of gp160 and GLUT4. Despite the marked decrease in gp160 levels in the GLUT4-containing compartment, insulin-stimulated translocation was normal, while little gp160 appeared in the plasma membrane in response to insulin. The retention of gp160 in the high-density microsomes is apparently not due to a change in the glycosylation state of gp160 as measured by [3H]mannose incorporation. It is concluded that, in rat adipocytes, gp160 is not required for insulin-stimulated translocation, but may be necessary for constitutive trafficking of the GLUT4-containing vesicle.
Filippis
A
A
The University of Melbourne, Department of Medicine, Royal Melbourne Hospital, Parkville 3050, Victoria, Australia.
Clark
S
S
Proietto
J
J
D015720:5'-Nucleotidase / Q000378:metabolism; D017667:Adipocytes / Q000378:metabolism; D000626:Aminopeptidases / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D003847:Deoxyglucose / Q000378:metabolism; D004705:Endocytosis; D005089:Exocytosis; D005944:Glucosamine / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D051275:Glucose Transporter Type 4; D006031:Glycosylation; D007328:Insulin / Q000494:pharmacology*; D046911:Macromolecular Substances; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley
D051275:Glucose Transporter Type 4; D007328:Insulin; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D003847:Deoxyglucose; D015720:5'-Nucleotidase; D000626:Aminopeptidases; C097037:GLUT4-associated glycoprotein gp160, rat; D005947:Glucose; D005944:Glucosamine